Vista Home Premium.
Worth it, less effort.
I really didn't see the point in paying extra for flashy wallpapers and some security thing for my HDD which can't even be stolen by my family, so I got Home Premium.
It isn't really worth it for Ultimate unless you REALLY need it.
Get ready, to get forgeted.
/smack
I've been using 64-bit Home Premium SP1 now for a month, and it's actually better than 32 bit XP Professional SP3. What took me 45 minutes to convert a movie from .avi to .mp4 now takes 15 minutes.
Copying and pasting my entire My Documents folder on XP took an hour.
Copying and pasting it on Vista took <15 minutes.
Basically, 64 bit Vista is worth it.
I'm not sure about
Ultimate though, but that's just me.
Just make sure you get 64-bit Vista drivers, turn off User Account Control and know your way around Vista (which will take a day or two maybe), and you'll be fine.